Leading and lagging DNA strands exist at a replication fork because .A. the DNA polymerase can add new nucleotides onto either the 3' end or the 5' end B. the two strands of DNA are antiparallel, and DNA polymerase can only add new nucleotides onto a 5' end C. the two strands of DNA are parallel and DNA polymerase can only add new nucleotides onto a 3' D. end the two strands of DNA can be either parallel or antiparallel the two strands of DNA are antiparallel, and DNA polymerase can only add new nucleotides onto a 3' end